feat(integrations): Deprecate pluggable integration classes

[mydea]

Instead, users should import & use the integration functions.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	77.28 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	68.59 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	62.23 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	32.61 KB (-0.02% 🔽)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.13 KB (+0.01% 🔺)
@sentry/browser - Webpack (gzipped)	22.48 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	74.94 KB (+0.07% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	66.57 KB (+0.07% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	32.41 KB (+0.14% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.18 KB (+0.23% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	209.64 KB (+0.05% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	97.7 KB (+0.09% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	72.32 KB (+0.12% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	35.44 KB (+0.12% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	68.98 KB (-0.01% 🔽)
@sentry/react - Webpack (gzipped)	22.52 KB (-0.02% 🔽)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	85.6 KB (-0.01% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	49.73 KB (-0.01% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	17.11 KB (0%)